Joe Hendrix, 35, killed 72-year-old Ronald Westbrook when the elderly man wandered onto the property of Hendrix’s fiancée in north Georgia early in the morning of Nov. 27, 2013, the Associated Press reports.

Hendrix told police that Westbrook had been knocking on the door and ringing the doorbell, prompting Hendrix go outside to confront him in the dark with his .40-caliber handgun while his fiancée called 911. Hendrix said he had asked Westbrook to stop and identify himself, but when the elderly man continued, Hendrix fired four warning shots before shooting Westbrook fatally.

Westbrook lived with his wife of 51 years and had wandered from their home earlier that night. A police officer saw Westbrook on the street about 2:30 a.m. and stopped him for questioning. Westbrook said he was just going to check some mailboxes nearby.

Alzheimer’s is a disease that causes memory loss.

District Attorney Herbert Franklin’s office called the incident a “tragic shooting death.”